It is planned to study the properties and possible alterations in activity under different physiological conditions of mammalian aminopropyltransferases. These enzymes are responsible for the synthesis of spermidine and spermine by the transfer of aminopropyl groups from decarboxylated S-adenosylmethionine to a suitable acceptor, but have been studied very little, particularly in comparison with the intensive studies of the preceding enzymes in the polyamine biosynthetic pathway, the decarbosylases forming decarboxylated SAM and putrescine. Also, our preliminary results suggest that under certain conditions, there may be aminopropyl transfers to another acceptor, probably protein and that this reaction is inhibited by spermidine. It is planned to: a. Purify and characterize the aminopropyltransferases from rat liver and prostate. Their affinities for decarboxylated SAM and for amine acceptors and the inhibition of activity by unphysiological diamines and by nucleosides related to SAM will be studied. b. To measure aminopropyltransferase activity in extracts from cells and tissues in which polyamine levels are known to be altered. These will include normal and transformed cells with serum stimulation of growth; cultured fibroblast exposed to tumor promoters; various rat tissues on starvation, rat heart during cardiac hypertrophy and male sex accessory glands on stimulation with adrogens. c. To measure cellular decarboxylated SAM levels. d. To characterize further the transfer of aminopropyl groups to protein and ascertain whether this reacton takes place in vivo. The experiments will be facilitated by the use of a rapid assay for aminopropyltransferase activity which measures the production of radioactive 5'-methylthioadenosine from methyl-labeled decarboxylated SAM in the presence of the appropriate amine.